The invention relates generally to microflow cytometry and more particularly to devices and methods for batch processing magnetic bead assays.
Flow cytometry is used in broad areas of technologies such as medical diagnostics. Such flow cytometers have generally been located in centralized laboratory settings and run by trained technicians. More recently laboratories are moving towards smaller, less expensive instruments that provide a greater level of automation. Microfluidics has played an important role in this transition, providing simpler methods of sample injection, cell sorting, and optical interrogation. However, sample preparation for these microdevices remains an unmet challenge before such devices are adapted for point-of-care and on-site environments.
For example, current magnetic bead based assays use a large permanent magnet that traps beads contained within microliter-sized tubes and wells for solution-based assays. These magnetic bead traps, that are meant to capture beads in a fluid flow, use the large permanent magnet for pre-concentration upstream from a standard flow cytometer. However, as with most bulk bead traps, detection limits are set by the reaction kinetics on the bulk surface used to capture beads. Current magnetic bead assays are inefficient at high bead counts because the beads clump together, which blocks binding sites on the beads. When performing surface reactions on beads trapped within continuous flow channels, bead clumping during magnetic bead immobilization interferes with surface binding reactions and downstream analysis. Although others have attempted to trap a small number of beads in parallel microfluidic reaction chambers for better control over bead reactions, this approach requires that the reactions take place in nanoliter-sized compartments, which severely limits throughput.
Others have also created magnetic arrays either using miniaturized electromagnets or passive arrays of permanent magnetic elements. However, electromagnets are too expensive and require too much power to employ them in magnetic bead assays. Similarly, passive arrays of permanent magnet elements are not practical for magnetic bead assays because the number of beads, on each magnet surface in a passive array on each individual magnetic surface, cannot be controlled. Thus, neither approach can be used to optimize and batch process magnetic bead reactions.
In addition, although studies have been conducted on flow cell arrays for capturing rare cells on arrays of immuno-functionalized posts, no methods exist to extend these studies to magnet bead-based approaches.